1. Field of the Invention
This invention relates generally to the art of studying the physical properties of microscopic particles carried in suspension and more particularly is concerned with improved structure for obtaining signals from particles passing through a scanning aperture mounted in a module without extraneous interference from other particles.
2. Description of the Prior Art
The Related Patent discusses a specific problem which occurred during use of the aperture tube disclosed in U.S. Pat. No. 3,299,354. The structure of U.S. Pat. No. 3,299,354 substantially decreased the possibility of undesirable spurious particle reading and count signals which sometimes occurred in prior art devices. The aperture tube was self-cleaning in that the suspension in the immediate vicinity of the aperture was kept relatively free of extraneous particles. Despite the self-cleaning aspect of the structure of U.S. Pat. No. 3,299,354, eddy currents of fluid in the aperture tube at the downstream end of the primary bore could occur, and these eddy currents swirled into the secondary bore immediately adjacent the primary bore. The structure of U.S. Pat. No. 3,746,976 (U.S. Pat. No. RE. 28,558) improved on the structure of U.S. Pat. No. 3,299,354 with the addition of a pump device interposed between the first and second chambers of the aperture tube to produce a closed system in which there are no inlets or outlets other than the primary bore in the first chamber. In the structure of the Related Patent, several specific alternate forms of aperture retaining members or tubes are disclosed in which the spurious signal producing zone of the aperture tube continuously is washed simultaneously with passage of the suspension through the aperture such that particles which have been measured within the aperture and thereafter passing out of the same immediately are swept out of the spurious signal producing zone by the particle free liquid and moved into the outlet chamber.
Specifically in connection with the disclosure of the Related Patent, one of the aperture retaining members described therein is a generally U-shaped tube with the aperture positioned in the side of one leg of the tube. A V-shaped restriction is formed in the wall of the U tube opposite the aperture to increase the flow velocity of electrolyte as it passes behind the aperture. Clean electrolyte flows down one leg of the tube and provides a continuous washing or sweep flow effect behind the aperture by reason of the restriction. The wash or sweep flow electrolyte together with the sample which has been drawn through the aperture then leaves the U tube through the exit leg. The spurious signal producing zone behind the aperture proximate the V-shaped restriction is continuously washed to maintain the same free of particles.
The basic concept of the referred-to structure of the Related Patent is satisfactory for accomplishing the object of continuously washing the spurious signal producing zone in the aperture retaining member but is relatively fragile and awkward for use in sophisticated commercial structures. The structure of the present application utilizes the concept of the Related Patent in a more practical module adapted specifically for use in presently developed sophisticated particle analyzing devices.
The technology represented by the pioneer U.S. Pat. No. 2,656,508 has burgeoned with world-wide utilization of the electronic particle studying apparatus disclosed therein. The vessel comprising a simple test tube with an aperture in its side walls shown in U.S. Pat. No. 2,656,508 was just that in commercial instruments made in the infancy of the art and many of the instruments of today still utilize this specific structure. The vessel has over the years become known as an "aperture tube". Added functions of improved versions of the well-known aperture tube have in many cases resulted in physical changes that render the same almost unrecognizable. In the structure of this application it has been deemed appropriate to refer to the aperture tube as being part of a "module" because of its relationship to other structure and its many added functions as well as its departure from tubular appearance, but it should be kept in mind in the reading of this specification and claims that the primary and most basic function of the module is common to that of the classic aperture tube -- hence, it is the equivalent thereof with respect to this basic function. its